1. Field of the Invention
The present invention generally relates to battery operated lamps and, more particularly, to battery operated fluorescent lamps having built-in battery recharging capability and operable from either a 120 VAC or 12 VDC source of power.
2. Description of the Prior Art
Portable incandescent lamps, which operate by using an electric current to heat a filament, have been readily available for use as flashlights, task lights or work lights (e.g., ‘drop’ lights), camp lights, and the like. While generally reliable and reasonably durable, incandescent lamps are inefficient, whether operated from AC or DC voltage sources. Further, battery operated incandescent lamps are generally limited in the amount of light output because of the inefficiency of heated filament technology. Other disadvantages of incandescent lamps include the susceptibility of filaments to breakage and the heat produced, which can be uncomfortable when used in close quarters.
Portable fluorescent lamps have also been readily available for use as flashlights, task lights or work lights (e.g., ‘drop’ lights), camp lights, and the like. As is well known, fluorescent lamps are relatively efficient compared to incandescent lights, but they require a ballast device of some type to provide both a high starting voltage to ionize the gas within the bulb and a current-limiting impedance to limit the current flowing between the lamp terminals after the gas becomes ionized and highly conductive. In conventional AC operated fluorescent lamps the ballast device is a relatively large, heavy inductor in series with the fluorescent bulb. The large inductor provides a high back EMF when the alternating supply current reverses in the inductor, which causes a high starting voltage to ionize the gas within the bulb. The large inductance also provides a substantial impedance to the flow of current through the bulb after the ionization takes place.
In conventional portable fluorescent lamps, a small fluorescent bulb rated at, e.g., four watts, can be illuminated effectively with a battery voltage of 7.5 to 9.0 volts and a small step-up converter circuit to produce the relatively high starting voltage required. For such a low power rating, the inductance required to limit the current after ionization is correspondingly small enough to allow a practical battery operated fluorescent lamp that is not too bulky or heavy. However, fluorescent bulbs rated at four watts or even six watts do not provide much more light than a typical seven watt incandescent night light. Further, at 7.5 volts DC, the five large, C or D-cell alkaline batteries typically used in such lamps, which may provide up to one hour of illumination between battery replacement or recharging, causes the lamp to be bulky and heavy.
There are higher rated fluorescent bulbs available, such as a 13 watt Compact Fluorescent Lamp (CFL) Bi-Pin bulb. Such a bulb provides much higher light output but requires that more power be delivered by the ballast circuit. With conventional technology, this requirement demands a larger ballast circuit and further limits the battery life. While battery technology is continually improving, 13 watt, battery powered, portable fluorescent lamps, to be practical to use, must rely on rechargeable batteries. Typically, the lamp, in order to keep the size and weight within practical limits, contains only the batteries, the bulb, and an electronic ballast circuit. After a relatively short duration of use, typically one hour, the batteries must be replaced or recharged on an external battery charger. A typical external battery charger may have substantial bulk and weight, especially if it operates from a standard wall outlet of 120 VAC. There is currently no known portable fluorescent lamp available that includes the batteries, ballast, and bulb that also includes a built-in AC-DC converter and battery charger in a compact, flashlight-sized, light-weight package.
What is needed is a higher efficiency, 13 watt portable fluorescent lamp that includes a built-in battery charger and operates off of either 120 VAC or 12 VDC power, yet is compact and light weight, i.e., approximately the size and weight of a conventional flashlight powered by two or three “D” cells. Further, the portable fluorescent lamp must be as easy to handle as a flashlight—i.e., have all the electronics and the battery pack housed in an enclosure approximately the same size as the handle portion of a conventional “D” cell flashlight having two cells. The design must accordingly produce very little heat so that it may be comfortably held by the handle that encloses the electronics. The handle must be small enough in diameter to hold easily and securely in the average-sized person's hand. Further, the battery charger built-in to the handle must be efficient enough to recharge the battery pack in under 90 minutes while the portable lamp is in use.